1. Field of the Invention
The present invention relates to an optical fiber refractometer which can be used, for example, to analyze minute liquid samples.
2. Description of Related Art
In the field of analytical chemistry, it has become well-known to use the physical property of refractive index of chemicals in order to characterize various materials. For example, mixtures of chemicals may be separated by various chromatographic techniques and ultimately sent into a refractive index detector for identification and quantitation.
Recent advances in the field have enabled researchers to separate samples having smaller and smaller volumes, so as to conserve quantities of scarce or precious samples. Unfortunately, conventional refractive index detectors for chromatography require relatively large amounts of sample and are not compatible with modern capillary liquid chromatographic systems for separation of the minute samples of the present time.
It is therefore desirable to reduce the sample volume of a refractive index detector to the point that minute amounts of samples may be accurately detected, measured and quantitated in the effluent of a modern liquid chromatograph.
At the present time, no commercially available refractive index detectors exist for analysis of sample effluent from capillary zone electrophoresis (CZE) analyzers. Again, the sample volume from CZE equipment is minute and presently available refractive index detectors suffer from inadequate minimum detection levels for use with CZE.
U.S. Pat. No. 3,513,319 to Broerman discloses a refractometer having spaced light conducting rods, which may be used as a detector in a chromatographic analyzer, wherein a bundle of fiber optic tubes, having the cladding removed, is used in place of a single transparent tube of the prior art, in order to improve sensitivity for chromatographic analyzer uses.
U.S. Pat. Nos. 4,981,338 and 4,988,863 to Bobb et al. disclose an optical fiber refractometer and a method of measuring the index of refraction of a liquid by launching light into a first end of an optical fiber at a selected non-zero angle with respect to the fiber axis, wherein said optical fiber is provided with a first cylindrical region, a second tapered region, a third cylindrical region of a lesser diameter than that of the first cylindrical region and a forth tapered region.
U.S. Pat. No. 3,999,857 to David et al. discloses a refractive index detector for gradient elution chromatography with means for indicating the rate of change of refractive index, comprising a waveguide, means for contacting said waveguide with a fluid, a light source and means to transmit light into said waveguide, means for detecting light exiting from said waveguide and means to automatically change the angle of incidence of the light entering said waveguide in response to changes of refractive index of the fluid.
The disclosures of the above-cited patents are incorporated herein by reference.